Oligoarylene Derivatives and Organic Electroluminescent Devices Made By Using The Same

ABSTRACT

There are provided oligoarylene derivatives capable of emitting blue light at high luminous efficiency which are represented by the following general formulae (1) to (4): 
         Ar   1   −Ch−Ar   2   (1) 
         Ch   1   −L−Ch   2   (2) 
         Ar   3 −( L   1 ) a   −Ch   3 −( L   2 ) b   −Ar   4   (3) 
         Ar   5   −Ch   4 −( Ar   7 ) n   −L   3 −( Ar   8 ) m   −Ch   5   −Ar   6   (4) 
     wherein Ch, Ch 1  and Ch 2  are respectively a group containing at least one substituted or unsubstituted condensed aromatic ring having 14 to 20 nuclear atoms; Ch 3 , Ch 4  and Ch 5  are respectively a substituted or unsubstituted arylene group having 14 to 20 nuclear atoms; Ar 1 , Ar 2 , Ar 3 , Ar 4 , Ar 5  and Ar 6  are respectively a substituted or unsubstituted aryl group having 5 to 30 nuclear atoms; Ar 7  and Ar 8  are respectively a substituted or unsubstituted arylene group having 5 to 30 nuclear atoms; L 1 , L 2  and L 3  are respectively a connecting group; and a, b, n and m are respectively an integer of 0 to 1, as well as organic electroluminescent devices using the same.

TECHNICAL FIELD

The present invention relates to oligoarylene derivatives and organicelectroluminescent devices made by using the same, and more particularlyto oligoarylene derivatives capable of emitting blue light at a highluminous efficiency and organic electroluminescent devices made by usingthe same.

BACKGROUND ART

The organic electroluminescent devices (hereinafter,“electroluminescent” is referred to merely as “EL”) are emitting devicesusing the principle that a phosphor or fluorescent substance emits lightby an energy of recombination between holes injected from an anode andelectrons injected from a cathode upon application of an electric fieldthereto. Since C. W. Tang, et al., of Kodak Company have reportedlow-voltage drive organic EL devices of a laminated type (C. W. Tang andS. A. Vanslyke, “Applied Physics Letters”, Vol. 51, p. 913, 1987, etc.),there have been made intense studies concerning organic EL devices madeof organic materials. The organic EL devices reported by Tang, et al.,include a luminescent layer made of tris(8-hydroxyquinolinol)aluminumand a hole transport layer made of a triphenyl diamine derivative. Thelaminated structure of these devices provides advantages such asenhanced injection efficiency of holes into the luminescent layer,enhanced production efficiency of excitons that are produced by blockingelectrons injected from a cathode and recombining the electrons withholes, and confinement of the excitons produced within the luminescentlayer. As the structure of such organic EL devices, there are well knowna two-layer structure including a hole transport (injection) layer andan electron transport luminescent layer, a three-layer structureincluding a hole transport (injection) layer, a luminescent layer and anelectron transport (injection) layer, etc. In these organic EL devicesof a laminated type, various structures and methods for productionthereof have been proposed in order to enhance an efficiency ofrecombination between holes and electrons injected.

In addition, as the luminescent materials for the above devices, thereare known chelate complexes such as tris(8-quinolinolato) aluminumcomplexes, coumarin derivatives, tetraphenyl butadiene derivatives,bis-styryl arylene derivatives and oxadiazole derivatives. It has beenreported that these luminescent materials emit blue to red light in avisible range, and it is therefore expected to apply these luminescentmaterials to production of color display devices (for example, JapanesePatent Application Laid-open Nos. Hei 8(1996)-239655, Hei 7(1995)-138561and Hei 3(1991)-200289, etc.).

However, there exist few blue emitting luminescent materials capable ofproviding highly-reliable and stable blue light-emitting devices. Ingeneral, the conventional blue emitting luminescent materials are easyto crystallize. For example, diphenyl anthracene shows a highcrystallinity nevertheless their high fluorescent quantum yield.Therefore, the use of such a compound as a luminescent material hasfailed to provide devices exhibiting a high luminous efficiency and ahigh reliability (C. Adachi, et al., “Applied Phys. Lett.”, 56, 799(1990)).

DISCLOSURE OF THE INVENTION

The present invention has been made for solving the above conventionalproblems. An object of the present invention is to provide oligoarylenederivatives capable of emitting blue light at a high luminous efficiencyas well as organic EL devices made by using the compounds.

As a result of extensive researches for accomplishing the above object,the inventors have found that organic EL devices made by using theoligoarylene derivatives represented by the following general formulae(1) to (4) as a luminescent material or a hole transport materialtherefor are capable of emitting blue light at a high luminousefficiency.

The present invention has been accomplished on the basis of the abovefinding.

Thus, the present invention provides an oligoarylene derivativerepresented by any of the following general formulae (1) to (4):

Ai ¹ −Ch−Ar ²  (1)

wherein Ch is a group containing at least one substituted orunsubstituted condensed aromatic ring having 14 to 20 nuclear carbonatoms; and Ar¹ and Ar2 are respectively a substituted or unsubstitutedaryl group having 5 to 30 nuclear atoms and may be the same or differentfrom each other,

Ch ¹ −L−Ch ²  (2)

wherein L is a connecting group; and Ch¹ and Ch² are respectively agroup containing at least one substituted or unsubstituted condensedaromatic ring having 14 to 20 nuclear carbon atoms and may be the sameor different from each other,

Ar³−(L ¹)_(a) −Ch ³−(L ²)_(b) −Ar ⁴  (3)

wherein Ch³ is a substituted or unsubstituted arylene group having 14 to20 nuclear carbon atoms;

L¹ and L² are respectively a connecting group and may be the same ordifferent from each other; a and b are respectively an integer of 0 to1; and

Ar³ and Ar⁴ are respectively a substituted or unsubstituted aryl grouphaving 5 to 30 nuclear atoms and may be the same or different from eachother with the proviso that when Ch³ is a substituted or unsubstitutedpyrene residue, Ar³ and/or Ar⁴ are respectively a substituted orunsubstituted β-naphthyl derivative, and

Ar ⁵ −Ch ⁴−(Ar ⁷)_(n) −L ³−(Ar ⁸)_(m) −Ch ⁵ −Ar ⁶  (4)

wherein L³ is a connecting group; Ch⁴ and Ch⁵ are respectively asubstituted or unsubstituted arylene group having 14 to 20 nuclear atomsand may be the same or different from each other;

A⁵ and Ar⁶ are respectively a substituted or unsubstituted aryl grouphaving 5 to 30 nuclear atoms and may be the same or different from eachother;

Ar⁷ and A⁸ are respectively a substituted or unsubstituted arylene grouphaving 5 to 30 nuclear atoms and may be the same or different from eachother; and n and m are respectively an integer of 0 to 1.

Also, the present invention provides an organic electroluminescentdevice comprising a cathode, an anode and an organic thin film layersandwiched between the cathode and the anode which is constituted of asingle layer or a plurality of layers including at least one luminescentlayer, wherein at least one layer of the organic thin film layercontains the oligoarylene derivative represented by any of the generalformulae (1) to (4) as a single component or a component of a mixture.

BEST MODE FOR CARRYING OUT THE INVENTION

The oligoarylene derivative of the present invention is represented bythe following general formula (1) or (2).

Ar ¹ −Ch−Ar ²  (1)

In the general formula (1), Ch is a group containing at least onesubstituted or unsubstituted condensed aromatic ring having 14 to 20nuclear carbon atoms.

Examples of the condensed aromatic ring represented by Ch includephenanthrene, pyrene, chrysene, triphenylene and perylene. Of thesecondensed aromatic rings, preferred are pyrene and chrysene.

Ar¹ and Ar² are respectively a substituted or unsubstituted aryl grouphaving 5 to 30 nuclear atoms, and may be the same or different from eachother.

Examples of the substituted or unsubstituted aryl group having 5 to 30nuclear atoms which is represented by Ar¹ and Ar² include phenyl,1-naphthyl, 2-naphthyl, 1-anthryl, 2-anthryl, 9-anthryl, 1-phenathryl,2-phenathryl, 3-phenathryl, 4-phenathryl, 9-phenathryl, 1-naphthacenyl,2-naphthacenyl, 9-naphthacenyl, 1-pyrenyl, 2-pyrenyl, 4-pyrenyl,2-biphenylyl, 3-biphenylyl, 4-biphenylyl, p-terphenyl-4-yl,p-terphenyl-3-yl, p-terphenyl-2-yl, m-terphenyl-4-yl, m-terphenyl-3-yl,m-terphenyl-2-yl, o-tolyl, m-tolyl, p-tolyl, p-t-butylphenyl,p-(2-phenylpropyl)phenyl, 3-methyl-2-naphthyl, 4-methyl-1-naphthyl,4-methyl-1-anthryl, 4′-methylbiphenylyl, 4″-t-butyl-p-terphenyl-4-yl andfluorenyl.

Ch ¹ −L−Ch ²  (2)

In the general formula (2), L is a connecting group. Example of theconnecting group include groups having a structure of a single bond,methylene, ethylene, dimethylmethylene, diphenylmethylene, lactone ringor peptide. Of these connecting groups, preferred is a single bond.These groups may have substituent groups.

Examples of the condensed aromatic rings represented by Ch¹ and Ch² arethe same as those condensed aromatic rings represented by the above Ch.

The above general formula (1) is preferably represented by the generalformula (3).

In the general formula (3), Ch³ is a substituted or unsubstitutedarylene group having 14 to 20 nuclear carbon atoms. Examples of thearylene group represented by Ch³ include divalent residues ofphenanthrene, pyrene, chrysene, triphenylene and perylene. Of thesearylene groups, preferred are divalent residues of pyrene and chrysene.

L¹ and L² are respectively a connecting group and may be the same ordifferent from each other. Examples of the connecting groups representedby L¹ and L² are the same as those connecting groups represented by theabove L. These connecting groups may have substituent groups. Thesymbols a and b are respectively an integer of 0 to 1.

Ar³ and Ar⁴ are respectively a substituted or unsubstituted aryl grouphaving 5 to 30 nuclear atoms, and may be the same or different from eachother. Examples of the aryl group are the same as those represented bythe above Ar¹ and Ar².

However, when Ch³ is a substituted or unsubstituted pyrene residue, Ar³and/or Ar⁴ are respectively a substituted or unsubstituted β-naphthylderivative.

The above general formula (2) is preferably represented by the generalformula (4).

In the general formula (4), L³ is a connecting group. Examples of theconnecting group represented by L³ are the same as those connectinggroups represented by the above L. The connecting group may havesubstituent groups.

Ch⁴ and Ch⁵ are respectively a substituted or unsubstituted arylenegroup having 14 to 20 nuclear atoms, and may be the same or differentfrom each other. Examples of the arylene group include phenanthrylene,pyrenylene, chrysenylene, triphenylenylene and perylenylene. Of thesearylene groups, preferred are pyrenylene and chrysenylene.

Ar⁵ and Ar⁶ are respectively a substituted or unsubstituted aryl grouphaving 5 to 30 nuclear atoms and may be the same or different from eachother. Examples of the aryl group are the same as those groupsrepresented by the above Ar¹ and Ar².

Ar⁷ and Ar⁸ are respectively a substituted or unsubstituted arylenegroup having 5 to 30 nuclear atoms and may be the same or different fromeach other. Examples of the arylene group are divalent groups of thearyl groups represented by the above Ar¹ and Ar². The symbols n and mare respectively an integer of 0 to 1.

Examples of the substituent groups of the above groups represented byCh, Ch¹ to Ch⁵ and Ar¹ to Ar8 include halogen atoms, hydroxyl, nitro,cyano, alkyl, aryl, cycloalkyl, alkoxy, aromatic heterocyclic groups,aralkyl, aryloxy, arylthio, alkoxycarbonyl and carboxyl.

Examples of the substituent groups of the groups represented by theabove L and L¹ to L³ are also the same as described above.

Specific examples of the oligoarylene derivatives represented by theabove general formulae (1) to (4) are as follows, though they are notlimited to these compounds.

The oligoarylene derivative of the present invention is preferably usedas a luminescent material and a hole transport material of organic ELdevices.

The organic EL device of the present invention comprises a cathode, ananode and an organic thin film layer sandwiched between the cathode andthe anode which is constituted of a single layer a plurality of layersincluding at least one luminescent layer wherein at least one layer ofthe organic thin film layer contains the oligoarylene derivativerepresented by any of the general formulae (1) to (4) as a singlecomponent or a component of a mixture.

The luminescent layer preferably contains the oligoarylene derivativerepresented by any of the general formulae (1) to (4), and morepreferably the luminescent layer contains the oligoarylene derivative asa main component.

Also, in the organic EL device of the present invention, morepreferably, the luminescent layer further contains an arylamine compoundand/or a styrylamine compound.

Examples of the preferred styrylamine compound include those compoundsrepresented by the following general formula (A):

wherein Ar⁹ is a group selected from the group consisting of phenyl,biphenyl, terphenyl, stilbene and distyrylaryl; Ar¹⁰ and Ar¹¹ arerespectively a hydrogen atom or a C₆ to C₂₀ aromatic group; Ar⁹, Ar¹⁰and Ar¹¹ may be substituted; c is an integer of 1 to 4; and at least oneof Ar10 and Ar¹¹ may be substituted with styryl.

Examples of the C₆ to C₂₀ aromatic group include phenyl, naphthyl,anthranyl, phenathryl and terphenyl.

Examples of the preferred arylamine compound include those compoundsrepresented by the following formula (B):

wherein Ar¹² to Ar¹⁴ are respectively a substituted or unsubstitutedaryl group having 5 to 40 nuclear carbon atoms; and d is an integer of 1to 4.

Examples of the aryl group having 5 to 40 nuclear carbon atoms includephenyl, naphthyl, anthranyl, phenanthryl, pyrenyl, coronyl, biphenyl,terphenyl, pyrrolyl, furanyl, thiophenyl, benzothiophenyl, oxadiazolyl,diphenylanthranyl, indolyl, carbazolyl, pyridyl, benzoquinolyl,fluoranthenyl, acenaphthofluoranthenyl and stilbene. Meanwhile, examplesof the preferred substituent groups of these aryl groups include C₁ toC₆ alkyl groups such as ethyl, methyl, i-propyl, n-propyl, s-butyl,t-butyl, pentyl, hexyl, cyclopentyl and cyclohexyl, C₁ to C₆ alkoxygroups such as ethoxy, methoxy, i-propoxy, n-propoxy, s-butoxy,t-butoxy, pentoxy, hexyloxy, cyclopentoxy and cyclohexyloxy, aryl groupshaving 5 to 40 nuclear atoms, amino groups substituted with aryl groupshaving 5 to 40 nuclear atoms, ester groups substituted with aryl groupshaving 5 to 40 nuclear atoms, ester groups having a C₁ to C₆ alkylgroup, cyano, nitro and halogen atoms.

The organic thin film layer may have a hole transport layer containingthe oligoarylene derivative represented by any of the general formulae(1) to (4) as a single component or a component of a mixture, especiallypreferably as a main component thereof.

In the followings, the structure or configuration of the organic ELdevice according to the present invention is explained.

Typical structures of the organic EL device of the present invention areas follows.

(1) Anode/luminescent layer/cathode

(2) Anode/hole injection layer/luminescent layer/cathode

(3) Anode/luminescent layer/electron injection layer/cathode

(4) Anode/hole injection layer/luminescent layer/electron injectionlayer/cathode

(5) Anode/organic semiconductor layer/luminescent layer/cathode

(6) Anode/organic semiconductor layer/electron barrier layer/luminescentlayer/cathode

(7) Anode/organic semiconductor layer/luminescent layer/adhesionmodifying layer/cathode

(8) Anode/hole injection layer/hole transport layer/luminescentlayer/electron injection layer/cathode

(9) Anode/insulating layer/luminescent layer/insula ting layer/cathode

(10) Anode/inorganic semiconductor layer/insulating layer/luminescentlayer/insulating layer/cathode

(11) Anode/organic semiconductor layer/insulating layer/luminescentlayer/insulating layer/cathode

(12) Anode/insulating layer/hole injection layer/hole transportlayer/luminescent layer/insulating layer/cathode

(13) Anode/insulating layer/hole injection layer/hole transportlayer/luminescent layer/electron injection layer/cathode

Among these structures, the structure (8) is usually preferably usedthough not particularly limited thereto.

The organic EL device is usually formed on a light-transmittablesubstrate. The light-transmittable substrate has a function ofsupporting the organic EL device, and preferably exhibits a lighttransmittance of 50% or more in a visible range of 400 to 700 nm.Further, the light-transmittable substrate usable in the presentinvention more preferably has a smooth surface.

Examples of the suitable light-transmittable substrate include a glassplate and a synthetic resin plate. Specific examples of the glass plateinclude plates made of soda lime glass, barium/strontium-containingglass, lead glass, aluminosilicate glass, borosilicate glass, bariumborosilicate glass, quartz, etc. Specific examples of the syntheticresin plate include plates made of polycarbonate resins, acrylic resins,polyethylene terephthalate resins, polyether sulfide resins, polysulfoneresins, etc.

Next, the anode is preferably made of electrode substances such asmetals, alloys, electrically conductive compounds or mixtures thereofwhich have a large work function of 4 eV or more. Specific examples ofthe electrode substances for the anode include metals such as Au, andconductive materials such as CuI, ITO (indium tin oxide), SnO₂, ZnO andIn—Zn—O. The anode may be produced by forming these electrode substancesinto a thin film by vapor deposition method or sputtering method. Theanode preferably has such a property that when light emitted from theabove luminescent layer is taken outside from the anode, a transmittancethereof relative to the emitted light is 10% or higher. Also, the anodepreferably has a sheet resistance of several hundred Ω/□ or lower, andthe thickness thereof may be selected from the range of usually from 10nm to 1 μm and preferably from 10 to 200 nm though it varies dependingupon the materials used therefor.

Next, the cathode is preferably made of electrode substances such asmetals, alloys, electrically conductive compounds or mixtures thereofwhich have a small work function of 4 eV or lower. Specific examples ofthe electrode substances for the cathode include sodium,sodium-potassium alloy, magnesium, lithium, magnesium-silver alloy,aluminum/aluminum oxide, Al/Li₂O, Al/LiO₂, Al/LiF, aluminum, lithiumalloys, indium and rare earth metals.

The cathode may be produced by forming these electrode substances into athin film by vapor deposition method or sputtering method.

When light emitted from the luminescent layer is taken outside from thecathode, a transmittance thereof relative to the emitted light ispreferably 10% or higher. Also, the cathode preferably has a sheetresistance of several hundred Ω/□ or lower, and the thickness of thecathode is usually from 10 nm to 1 μm and preferably from 50 to 200 nm.

In the organic EL device of the present invention, at least one of apair of the thus produced electrodes is preferably provided on a surfacethereof with a chalcogenide layer, a metal halide layer or a metal oxidelayer (hereinafter, occasionally referred to merely as a “surfacelayer”). More specifically, the anode is provided on its surface facingthe luminescent layer, with a layer made of chalcogenide (including anoxide) of metals such as silicon and aluminum, and the cathode isprovided on its surface facing the luminescent layer, with a metalhalide layer or a metal oxide layer. The provision of these surfacelayers ensures stable operation of the device.

Examples of the preferred chalcogenide include SiOx (1≦X≦2), AlOx(1≦X≦1.5), SiON and SiAlON. Examples of the preferred metal halideinclude LiF, MgF₂, CaF₂ and fluorinated rare earth metals. Examples ofthe metal oxide include Cs₂O, Li₂O, MgO, SrO, BaO and CaO.

Further, in the organic EL device of the present invention, at least oneof a pair of the thus produced electrodes is preferably provided on asurface thereof with a mixed region composed of an electron transportcompound and a reducing dopant, or a mixed region composed of a holetransport compound and an oxidizing dopant. With such an arrangement,the electron transport compound tends to be reduced into anions, so thatelectrons tend to be injected and transported from the mixed region intothe luminescent layer. In addition, since the hole transport compoundtends to be oxidized into cations, so that holes tend to be injected andtransported from the mixed region into the luminescent layer. Examplesof the preferred oxidizing dopant include various Lewis acids andacceptor compounds. Examples of the preferred reducing dopant includealkali metals, alkali metal compounds, alkali earth metals rare earthmetals and compounds thereof.

In the organic EL device of the present invention, the luminescent layerhas:

(1) Injection function: function capable of injecting holes from theanode or hole injection layer, or injecting electrons from the cathodeor electron injection layer, upon application of an electric filedthereto;

(2) Transport function: function capable of moving the injected electriccharges (electrons and holes) by a force of the electric field applied;and

(3) Luminescent function: function capable of providing a site forrecombination between the electrons and holes which leads to lightemission.

The luminescent layer may be formed by conventionally known methods suchas vapor deposition method, spin-coating method and LB method. Theluminescent layer is more preferably made of a molecular depositionfilm. Here, the “molecular deposition film” means a thin film depositedfrom a material compound in the form of a gas phase, or a filmsolidified from a material compound in the form of a solution or aliquid phase. The molecular deposition film is usually distinguishedfrom those thin films formed by LB method (molecular accumulation films)owing to the difference in coagulated structure and higher-orderstructure as well as the difference in functions due to thesestructures.

In addition, as described in Japanese Patent Application Laid-open No.Sho 57(1982)-51781, the luminescent layer may also be produced bydissolving a binder such as resins and the material compound in asolvent and then forming the resultant solution into a thin film by aspin-coating method, etc.

In the present invention, the luminescent layer may contain, in additionto the above luminescent material made of the oligoarylene derivative ofthe present invention, other known luminescent materials, if desired,unless the addition of these materials adversely affects the objects ofthe present invention. Alternatively, a luminescent layer containing theother known luminescent materials may be laminated on the luminescentlayer made of the luminescent material containing the oligoarylenederivative of the present invention.

Next, the hole injection/transport layer serves for aiding injection ofholes into the luminescent layer and transporting the injected holes upto a light emission region, and has a large hole mobility and anionization energy as small as usually 5.5 eV or less. The holeinjection/transport layer is preferably made of a material capable oftransporting holes into the luminescent layer at a lower fieldintensity, and more preferably such a material having, for example, ahole mobility of at least 10⁻⁶ cm²/V·s upon application of an electricfield of 10⁴ to 10⁶ V/cm. As such a hole transport material, there maybe usefully used the oligoarylene derivative of the present invention.In addition, the hole transport material may be optionally selected fromthose ordinarily used as a transport material for electric charge, i.e.,holes among conventional photoconductive materials, as well as knownmaterials used for a hole injection layer of organic EL devices.

The hole injection/transport layer may be produced by forming the holeinjection/transport material into a thin film by known methods such as,for example, vapor deposition method, spin-coating method, castingmethod and LB method. In this case, the thickness of the holeinjection/transport layer is not particularly limited, and usually inthe range of 5 nm to 5 μm.

The electron injection/transport layer serves for aiding injection ofelectrons into the luminescent layer and transporting the injectedelectrons up to the light emission region, and has a large electronmobility. Further, the adhesion modifying layer may be made of amaterial having a good adhesion to especially the cathode among theelectron injection materials. Examples of the suitable material used forthe electron injection layer include 8-hydroxyquinoline and metalcomplexes of derivatives thereof. Specific examples of8-hydroxyquinoline and metal complexes of derivatives thereof includemetal chelate oxinoid compounds containing a chelate of oxine such as,generally, 8-quinolinol and 8-hydroxyquinoline. For example,tris(8-quinolinol)aluminum may be used as the electron injectionmaterial.

Also, in general, the organic EL device tends to suffer from defects ofpixels due to leakage or short since an electric field is applied to theultra-thin film. In order to prevent this problem, a pair of a thininsulating layer may be inserted between the pair of electrodes.

Examples of materials for the insulating layer include aluminum oxide,lithium fluoride, lithium oxide, cesium fluoride, cesium oxide,magnesium oxide, magnesium fluoride, calcium oxide, calcium fluoride,aluminum nitride, titanium oxide, silicon oxide, germanium oxide,silicon nitride, boron nitride, molybdenum oxide, ruthenium oxide andvanadium oxide. These materials may be used in the form of a mixture ora laminate of any two or more thereof.

Then, the organic EL device of the present invention may be produced,for example, by forming the anode and the luminescent layer togetherwith the hole injection layer and the electron injection layer, ifrequired, and then finally forming the cathode, using the abovematerials and methods. Alternatively, the organic EL device may beproduced in the reverse order starting from formation of the cathode andterminating at formation of the anode.

In the followings, the production of the organic EL device formed on alight-transmittable substrate which is successively provided with ananode, a hole injection layer, a luminescent layer, an electroninjection layer and a cathode is explained.

First, a thin film made of an anode material is formed on an appropriatelight-transmittable substrate by a vapor deposition method or asputtering method such that the thickness thereof is 1 μm or lower andpreferably 10 to 200 nm to thereby form an anode. Next, a hole injectionlayer is formed on the anode. The hole injection layer may be formed bythe above-mentioned vacuum deposition method, spin-coating method,casting method or LB method. Of these methods, the vacuum depositionmethod is preferred since this method provides a uniform film that isfree from defects such as occurrence of pinholes. In the case where thehole injection layer is formed by the vacuum deposition method, thedeposition conditions may vary depending upon compounds (materials forthe hole injection layer) used, crystal structure or recombinationstructure of the aimed hole injection layer, etc. In general, thedeposition conditions are preferably selected such that the depositionsource temperature is 50 to 450° C., the vacuum degree is 10⁻⁷ to 10⁻³torr, the deposition velocity is 0.01 to 50 nm/s, the substratetemperature is −50 to 300° C., and the thickness of layer to bedeposited is 5 nm to 5 μm.

Then, a luminescent layer is formed on the hole injection layer. Theluminescent layer may be produced from the luminescent material of thepresent invention, specifically may also be produced by forming theluminescent material into a thin film by vacuum deposition method,spin-coating method, casting method or the like. Of these methods, thevacuum deposition method is preferred since this method provides auniform film that is free from defects such as occurrence of pinholes.In the case where the luminescent layer is formed by the vacuumdeposition method, the deposition conditions may vary depending uponcompounds used. In general, the deposition conditions are preferablyselected from the same ranges as used upon formation of the holeinjection layer. The thickness of the luminescent layer is preferably 10to 40 nm.

Next, an electron injection layer is formed on the luminescent layer.The electron injection layer is also preferably formed by the vacuumdeposition method for providing a uniform film similarly to theformation of the hole injection layer and the luminescent layer. Thedeposition conditions may be selected from the same ranges as used uponformation of the hole injection layer and the luminescent layer.

Finally, a cathode is laminated on the electron injection layer toobtain the organic EL device. The cathode is made of metal and may beformed by vacuum deposition method or sputtering method. Of thesemethods, the vacuum deposition method is preferred in order to preventdamage to the underlying organic substance layer upon formation of thefilm.

The production of the organic EL device including the step of formingthe anode up to the step of forming the cathode is preferably completedby one vacuum drawing stroke.

When a D.C. voltage is applied to the organic EL device, the anode isconnected to a positive (+) polarity and the cathode is connected to anegative polarity (−) and a voltage of 3 to 40 V is appliedtherebetween, so that light is emitted from the organic EL device. Onthe contrary, even though the anode is connected to a negative polarity(−) and the cathode is connected to a positive (+) polarity, no light isemitted from the organic EL device. Further, in the case where analternating current is applied to the anode and cathode, light emissionis observed only when the anode is a positive (+) polarity and thecathode is a negative polarity (−). The alternating current applied mayhave an optional waveform.

The present invention will be described in more detail by reference tothe following examples. However, it should be noted that the followingexamples are only illustrative and not intended to limit the inventionthereto.

EXAMPLE 1 Synthesis of 2,6-bis(2-naphthyl)pyrene (CH1)

Under an argon atmosphere, 3 g of 2,6-dibromopyrene, 3.6 g of2-naphthaleneboric acid available from Tokyo Kasei Co., Ltd., and 0.36 gof tetrakis(triphenylphosphine)palladium (0) available from HiroshimaWako Co., Ltd., were dissolved in 100 mL of toluene. The resultantsolution was mixed with a solution prepared by dissolving 5 g of sodiumcarbonate in 24 mL of water, and the mixed solution was refluxed for 10h and allowed to stand over one night.

The obtained reaction mixture was filtered and then successively washedwith water, methanol and acetone, thereby obtaining 2.9 g of alight-yellow solid.

As a result of the measurement for FD-MS (field desorption massanalvsis) of the obtained compound, it was confirmed that m/z=44 wasobtained relative to C₃₆H₂₂=454, and, therefore, the compound wasidentified to be 2,6-bis(2-naphthyl)pyrene (CH1) (yield: 77%).

EXAMPLE 2 Synthesis of 6,12-bis(1-naphthyl)chrysene (CH2)

Under an argon atmosphere, 3 g of 6,12-dibromochrysene, 4 g of1-naphthaleneboric acid available from Tokyo Kasei Co., Ltd., and 0.36 gof tetrakis(triphenylphosphine)palladium (0) available from HiroshimaWako Co., Ltd., were dissolved in 100 mL of toluene. The resultantsolution was mixed with a solution prepared by dissolving 5 g of sodiumcarbonate in 24 mL of water, and the resultant mixed solution wasrefluxed for 10 h and allowed to stand over one night.

The obtained reaction mixture was filtered and then successively washedwith water, methanol and acetone, thereby obtaining 3.2 g of alight-yellow solid.

As a result of the measurement for FD-MS of the obtained compound, itwas confirmed that m/z=480 was obtained relative to C₃₈H₂₄=480, and,therefore, the compound was identified to be6,12-bis(1-naphthyl)chrysene (CH2) (yield: 85%).

EXAMPLE 3 Synthesis of 6,12-bis(9-phenathryl)chrysene (CH3)

Under an argon atmosphere, 3 g of 6,12-dibromochrysene, 5 g of9-phenathreneboric acid available from Tokyo Kasei Co., Ltd., and 0.36 gof tetrakis(triphenylphosphine)palladium (0) available from HiroshimaWako Co., Ltd., were dissolved in 100 mL of toluene. The resultantsolution was mixed with a solution prepared by dissolving 5 g of sodiumcarbonate in 24 mL of water, and the resultant mixed solution wasrefluxed for 10 h and allowed to stand over one night.

The obtained reaction mixture was filtered and then successively washedwith water, methanol and acetone, thereby obtaining 4.2 g of alight-yellow solid.

As a result of the measurement for FD-MS of the obtained compound, itwas confirmed that m/z=580 was obtained relative to C₁₆H₂₈=580, and,therefore, the compound was identified to be6,12-bis(9-phenathryl)chrysene (CH3) (yield: 93%).

EXAMPLE 4 Synthesis of 6,12-bis(2-terphenyl)chrysene (CH4)

Under an argon atmosphere, 3 g of 6,12-dibromochrysene, 5 g of2-terphenylboric acid and 0.36 g oftetrakis(triphenylphosphine)palladium (0) available from Hiroshima WakoCo., Ltd., were dissolved in 100 mL of toluene. The resultant solutionwas mixed with a solution prepared by dissolving 5 g of sodium carbonatein 24 mL of water, and the resultant mixed solution was refluxed for 10h and allowed to stand over one night.

The obtained reaction mixture was filtered and then successively washedwith water, methanol and acetone, thereby obtaining 4.2 g of alight-yellow solid.

As a result of the measurement for FD-MS of the obtained compound, itwas confirmed that m/z=684 was obtained relative to C₅₄H₃₆=684, and,therefore, the compound was identified to be6,12-bis(2-terphenyl)chrysene (CH4) (yield: 79%).

EXAMPLE 5 Production of Organic El Device

A glass substrate with an ITO transparent electrode having a size of 25mm×75 mm×1.1 mm in thickness which was available from Geomatic Co.,Ltd., was subjected to ultrasonic cleaning for 5 min in isopropylalcohol, and then to UV ozone cleaning for 30 min. The thus cleanedglass substrate with transparent electrode lines was fitted to asubstrate holder of a vacuum deposition apparatus. First, a 60 nm-thickfilm made of the below-mentionedN,N′-bis(N,N′-diphenyl-4aminophenyl)-N,N-diphenyl-4,4′-diamino-1,1′-biphenyl (hereinafter referred to merely “TPD232 film”) was formed on asurface of the glass substrate on which the transparent electrode lineswere formed, such that the transparent electrode was covered therewith.The thus formed TPD232 film had a function as a hole injection layer.Successively, a 20 nm-thick film made of the below-mentionedN,N,N′,N′-tetra(4-biphenyl)diaminobiphenylene (hereinafter referred tomerely as “TBDB film”) was formed on the TPD232 film. The thus obtainedTBDB film had a function as a hole transport layer. Further, CH1 as aluminescent material (host material) was vapor-deposited on the TBDBfilm to form a 40 nm-thick CH1 film, and at the same time, thebelow-mentioned styryl-containing amine compound D1 as a luminescentmolecule (dopant) was vapor-deposited thereon at a weight ratio of CH1to D1 of 40:2. The thus formed deposited film had a function as aluminescent layer. Then, a 10 nm-thick film made of the below-mentionedAlq was formed on the luminescent layer. The thus formed Alq film had afunction as an electron injection layer. Thereafter, Li as a reducingdopant (Li source available from SAES Getter S.p.A.) and Alq weresubjected to binary vapor deposition to form an Alq:Li film having athickness of 10 nm as an electron injection layer (cathode). Then,metallic Al was vapor-deposited on the Alq:Li film to form a metalcathode, thereby producing an organic EL device.

The thus obtained organic EL device was subjected to measurement of itsluminous efficiency near a luminance of 100 nit. The results are shownin Table 1.

EXAMPLE 6 Production of Organic El Device

The same procedure as in EXAMPLE 5 was repeated except for using thebelow-mentioned aromatic amine D2 as a dopant instead of thestyryl-containing amine compound D1, thereby producing an organic ELdevice. The obtained organic EL device was subjected to measurement ofits luminous efficiency. The results are shown in Table 1.

EXAMPLES 7 to 12 Production of Organic El Device

The same procedure as in EXAMPLE 5 was repeated except for using thehost material and the dopant as shown in Table 1, thereby producing anorganic EL device. The obtained organic EL device was subjected tomeasurement of its luminous efficiency. The results are shown in Table1.

COMPARATIVE EXAMPLE 1 Production of Organic El Device

The same procedure as in EXAMPLE 5 was repeated except for using thebelow-mentioned compound an1 as a host material instead of CH1, therebyproducing an organic EL device. The obtained organic EL device wassubjected to measurement of its luminous efficiency. The results areshown in Table 1.

COMPARATIVE EXAMPLE 2 Production of Organic El Device

The same procedure as in COMPARATIVE EXAMPLE 1 was repeated except forusing the aromatic amine D2 as a dopant instead of the styryl-containingamine compound D1, thereby producing an organic EL device. The obtainedorganic EL device was subjected to measurement of its luminousefficiency. The results are shown in Table 1.

TABLE 1 Luminous Luminescent layer efficiency Color of Host materialDopant (cd/A) emitted light Example 5 CH1 D1 11.1 Blue Example 6 CH1 D211.5 Blue Example 7 CH2 D1 10.5 Blue Example 8 CH2 D2 10.7 Blue Example9 CH3 D1 10.2 Blue Example 10 CH3 D2 10.4 Blue Example 11 CH4 D1 10.3Blue Example 12 CH4 D2 10.6 Blue Comparative an1 D1 9.0 Blue Example 1Comparative an1 D2 9.3 Blue Example 2

As shown in Table 1, it was confirmed that the organic EL devicesobtained in Examples 5 to 12 emitted blue light at a higher luminousefficiency as compared to those obtained in Comparative Examples 1 and2.

INDUSTRIAL APPLICABILITY

As described above, the organic EL device made by using the oligoarylenederivative according to the present invention can emit blue light at ahigh luminous efficiency. Therefore, the organic EL device of thepresent invention is useful as a full-color organic EL device.

1. An oligoarylene derivative represented by the following generalformula (2):Ch ¹ −L−Ch ²  (2) wherein L is a connecting group; and Ch¹ and Ch² arerespectively a group containing at least one substituted orunsubstituted condensed aromatic ring having 14 to 20 nuclear carbonatoms and may be the same or different from each other.
 2. Anoligoarylene derivative represented by the following general formula(4):Ar ⁵ −Ch ⁴−(Ar⁷)_(n) −L ³−(Ar ⁸)_(m) −Ch ⁵ −Ar ⁶  (4) wherein L³ is aconnecting group; Ch⁴ and Ch⁵ are respectively a substituted orunsubstituted arylene group having 14 to 20 nuclear atoms and may be thesame or different from each other; Ar⁵ and Ar⁶ are respectively asubstituted or unsubstituted aryl group having 5 to 30 nuclear atoms andmay be the same or different from each other; Ar⁷ and Ar⁸ arerespectively a substituted or unsubstituted arylene group having 5 to 30nuclear atoms and may be the same or different from each other; and nand m are respectively an integer of 0 to
 1. 3. The oligoarylenederivative according to claim 1, wherein the condensed aromatic ring ingeneral formula (2) is selected from the group consisting ofphenanthrene, pyrene, chrysene, triphenylene and perylene.
 4. Theoligoarylene derivative according to claim 2, wherein the arylene groupin Ch⁴ and Ch⁵ of the general formula (4) is a group selected from thegroup consisting of phenanthrylene, pyrenylene, chrysenylene,triphenylenylene and perylenylene.
 5. The oligoarylene derivativeaccording to claim 1, wherein the oligoarylene derivative is used as aluminescent material for organic electroluminescent devices.
 6. Theoligoarylene derivative according to claim 1, wherein the oligoarylenederivative is used as a hole transport material for organicelectroluminescent devices.
 7. An organic electroluminescent devicecomprising a cathode, an anode and an organic thin film layer sandwichedbetween the cathode and the anode which is constituted of a single layeror a plurality of layers including at least one luminescent layer,wherein at least one layer of the organic thin film layer contains theoligoarylene derivative as claimed in claim 1 as a single component or acomponent of a mixture.
 8. The organic electroluminescent deviceaccording to claim 7, wherein the luminescent layer contains theoligoarylene derivative.
 9. The organic electroluminescent deviceaccording to claim 7, wherein the luminescent layer consists essentiallyof the oligoarylene derivative.
 10. The organic electroluminescentdevice according to claim 7, wherein the luminescent layer furthercontains an arylamine compound.
 11. The organic electroluminescentdevice according to claim 7, wherein the luminescent layer furthercontains an styrylamine compound.
 12. The organic electroluminescentdevice according to claim 7, wherein the organic thin film layer has ahole transport layer containing the oligoarylene derivative as a singlecomponent or a component of a mixture.
 13. The organicelectroluminescent device according to claim 12, wherein the holetransport layer consists essentially of the oligoarylene derivative. 14.The organic electroluminescent device according to claim 7, wherein theorganic electroluminescent device emits a blue light.